In the course of welding stainless steel surfaces, chromium is depleted and thereby exposing iron causing localised discolouration which must be removed to restore the polished appearance to the stainless steel. Metallic oxides in the form of scale can also form on the surface during the welding process and these need to be cleaned away or otherwise removed.
Surface staining and weld scale on stainless steel parts can be removed using a pickling gel of toxic acids including hydrofluoric and nitric acids. This prior art method requires a significant amount of time and occupational health and safety risks result.
It is also known to use electrically activated stainless steel weld cleaning devices which utilise a non-conductive fabric sock that covers a solid or wire electrode. The sock acts as a separator between the electrode and the work piece as well as a reservoir for the acidic electrolyte cleaning solution.
The sock is saturated with the cleaning solution which provides a short electrically conductive path between the electrode and the work piece. The cleaning solution is heated by the passage of electrical current through it and becomes more chemically active thereby cleaning the metal surface.
One disadvantage with these prior art devices is that the fabric socks tend to dry out and then burn through with the heat of the process. Another disadvantage is that the electrode is essentially a rigid shape which cannot conform to the many odd shapes encountered in stainless steel fabricated constructions.
Another approach is to use a conductive brush which consists of a conductive receptacle from which extends a bundle of conductive filaments or fibres. However, such conductive brushes perform poorly as a brush bristle because the fibres tend to flop on their sides—particularly when wet with electrolyte—rather than presenting erect fibre ends as the working contact point.
Electricity travels along the shortest path so that the electric current will flow through the side of a fibre part way along its length where the fibre comes in contact with the metal surface being cleaned. This causes two problems—one is that the heat caused by the flow of electrical current through the side wall of the fibre tends to cut the fibre at the contact point. The second problem is that whereas this flow of electric current performs the desired effect of heating the immersion electrolyte thereby cleaning the metal surface, accurate control of the cleaning process is reduced due to the broad spread of the fibres. When working in corners, the electric current passes to the nearest contact point and thus the current reaching the full depth of the corner is significantly reduced. It is therefore difficult to clean properly two faced corners with three faced corners being even more difficult.